The aim of this proposal is to characterize the neural pathways that regulate the intestinal peristaltic reflex in humans and animals, in particular, to identify the peptide transmitters that control the sensory, modulatory and motor limbs of the reflex. We have devised techniques to measure the sensory and motor limbs of the reflex and neuropeptide release associated with each, and have used various probes (specific antisera and peptide antagonists, axonal and sensory neurotoxins and peptide immunoassay and receptor-specific bioassay) to establish the functional coupling between myenteric neuropeptides and each component of the reflex. We have also devised three preparations that provide complementary information: isolated myenteric ganglia to examine the interplay between neurons that project within the plexus (interneurons); muscle strips with axonal remnants only to examine the interplay between neurons that project into circular muscle; and cultures of neurons derived from isolated myenteric ganglia: this unique system permits predominant or exclusive expression of one neuropeptide, and thus, identifies the singular effects of myenteric peptides on release of the expressed peptide. Thus far, we have shown that VIP/PHI motor neurons mediate descending relaxation, and cholinergic and tachykinin (SP/SK) motor neurons mediate ascending contraction. We have also shown that opioid and somatostatin neurons act as modulatory neurons to enhance or restrain the activity of VIP neurons. In addition, we have obtained evidence from isolated ganglia for the existence of a feedback mechanism between somatostatin and VIP that would enable a segment to switch from relaxation to contraction during peristalsis. We now propose to examine the participation of other myenteric transmitters in the regulation of the peristaltic reflex. Preliminary studies using the preparations listed above, show that these transmitters exert precise modulatory effects on sensory and motor limbs of the reflex: somatostatin as a facilitatory neuropeptide acting via inhibition of opioid peptides; galanin as postjunctional synergist in descending pathways; GRP, CCK and NPY as prejunctional stimulatory or inhibitory modulators; GABA as stimulatory prejunctional modulator in ascending and descending pathways; serotonin, depending on receptor type, as prejunctional inhibitory or stimulatory modulator; and CGRP as sensory mediator. The approach has provided the first characterization of the peptide transmitters that regulate the peristaltic reflex in humans and animals.